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Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| A large sample of southern IRAS galaxies - Spectral classes and superclustering
Results are presented of an extensive spectroscopic survey of IRASgalaxies, in three Southern-Hemisphere fields totaling about 0.5 sr.Spectroscopic observations have been made of 527 galaxies which arecandidates for 474 IRAS sources. Together with published data, there arenow measured redshifts for almost 850 of the 1178 selected IRAS galaxiesin these fields. This measured sample includes nearly all galaxies athigh redshifts, and hense high infrared luminosities, within thesefields. Classification of more than 350 of these galaxies usingemission-line ratios and line widths shows that about 90 percent havestarburst characteristics. Two distinct groups of starburst galaxies inthe sample display forbidden O III-line intensities which significantlyexceed those observed in optically selected starburst galaxies. One ofthese groups, with strong N II forbidden lines, may be related to linersand/or Seyfert galaxies. The other, with weak N II forbidden-lineemission, displays unusually narrow lines; this group is interpreted interms of the youngest phase of starburst activity.
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